In recent years, every effort has been made to miniaturize semiconductor devices, and there has been a demand to form miniaturized interconnects (which may be simply referred to as micro-interconnects). As a method for forming such micro-interconnects, sidewall interconnect techniques (which may be simply referred to as sidewall processing) for forming interconnects on sidewalls of a pattern of an insulating layer are being studied. The use of the sidewall interconnect technique allows a repeated pattern of interconnects to be formed at a pitch half of that for the pattern of the insulating layer. Such sidewall interconnects may be provided in an interconnect area (which may also be referred to as a thin interconnect area) used for a memory cell portion.
For a reduction in the number of manufacturing steps, attempts have been made to simultaneously form such thin interconnect areas and interconnect areas for peripheral circuits and the like in which no micro-interconnects need to be formed (these interconnect areas may also be referred to as thick interconnect areas).
In this case, interconnect materials to be formed into thin interconnects and thick interconnects, respectively, are formed in the same step and are equal in film thickness. On the other hand, in thin interconnect areas, for which the above-described sidewall interconnect technique is used, the interconnect material is formed on the sidewalls of the pattern of the insulating layer. Thus, the height of the interconnects depends on the height of the pattern. In thick interconnect areas, in which no micro-interconnects need to be formed, the height of the interconnects depends on the film thickness of the interconnect material. Hence, the interconnects in the thin interconnect area are higher than those in the thick interconnect area.
As a result, if contact plugs (which may be simply referred to as contacts) are arranged both in the thin interconnect area and in the thick interconnect area, the height of the contact plug varies depending on the interconnect area. This disadvantageously makes the formation of the contact plugs (which may also be referred to as contact processing) more difficult.
Furthermore, the interconnects in the thick interconnect area are desirably thickened in order to reduce interconnect resistance. However, the film thickness of the interconnect material is determined by the line width of sidewall interconnects (half pitch) and the like. This disadvantageously reduces the film thickness of the interconnects in the thick interconnect area, increasing the resistance.
As described above, the formation of semiconductor devices with high quality interconnects has been difficult.